Split the vanilla beans lengthwise with a knife, place in a bottle and fill with the vodka or alcohol of your choice. Cap the jar and place in a cool, dark place for 6 to 9 months. Vodka will likely be ready in 6 months. Dark alcohols like rum take about 9 months.
After 6 to 9 months, draw off the top 1/3 of the alcohol. That is the extract that you will use. Refill the bottle with the same amount of alcohol. Wait 2 months and repeat.
3 vanilla beans will provide flavor for three years. After three years, add one bean per year. I started making my vanilla extract on Dec. 26, 2016.
The ratio is 1 vanilla bean to 4 ounces of alcohol. So, you could also do 1.5 beans to 6 ounces of alcohol, 2 beans to 8 ounces, etc.
The Hawaiian Vanilla Co. recommends 60 to 80 proof vodka. It can be cheap vodka. They also recommend trying this with rum, brandy and whiskey.